More particularly, the present invention is concerned with a slide valve or similar hydraulic control valve which can be used in hydraulic, especially hydrostatic, drive systems having load-sensing means, and equipped with parallel pressure regulators, or throttles and the like means, disposed in the branch lines or conduits which connect the individual consuming, load or demand points or locations with a common pump.
The parallel pressure regulators serve to ensure that the respective throttle-opening velocity is always in conformity with the clear or effective opening or flow cross section for the particular load, even in the case of simultaneous operation or actuation of several loads or taking place at several demand points, and independently of the pressures experienced at the individual demand points, as is known from German Patent Publication DE-OS No. 30 44 144.2.
The invention is also based on state of the art as represented by German Patent Publication DE-OS No. 34 13 866.
In the latter system, which has been found to be highly effective, there still arise some drawbacks. For one, the pressure in the common control line or conduit (load-sensing-signal or load-sensing pressure) is varied on actuation or contacting of a further parallel demand point. This actuation or contacting is carried out with a greater or incremental pressure due to the pressure of the spring against which the second auxiliary piston--which is disposed towards the outer end of the main piston in accordance with DE OS No. 34 13 866--is supported with respect to or in an exterior manner. Accordingly, the load-sensing signal will be affected by the system or demand pressure and by the pressure of this spring. The force of the spring contributes to the generation of a value which functions as an unreliable and undesirable load-sensing signal.
Furthermore, in the earlier valves there exists the danger that the operation or functioning will be detrimentally affected by forces due to the fluid flow and undue pressure differences.
The control valve can be employed in a hydraulic and the like drive system, said system including a variable-speed pump with at least one control element, and said control element being connected to a pump control piston arranged in a pump control cylinder. The position of the piston can be determined by a control pressure. The drive system can further include a conveying conduit connected to said pump, and a return conduit which leads to the respective reservoir. The drive system is also characterized by control elements, whereby at the conduit emanating from the pump are connected--by intervention of a respective branch line--several demand points which respectively can be connected to the conveying conduit by means of an in the respective branch line arranged, randomly movable valve, and in each branch line there is provided an adjustable parallel control throttle position or the like means.
The control or adjustment element of each of these parallel control throttle positions or means can be impacted on the one side by the pressure prevailing in the conveying branch-conduit and on the other side by the control pressure and a spring. The control pressure is substantially the same at the parallel control throttle locations at the associated demand points. The control pressure impacted side of the control element of the parallel control throttle location--via a control pressure branch conduit--is connected to a common control pressure conduit, whereby in the respective conveying pressure branch line, there is formed a controllable indicator throttle location in the valve. In the flow direction behind this indicator throttle location the control pressure branch line is connected. On at least one side of the piston in this there is provided a longitudinal bore in which is mounted an auxiliary piston which can be moved against the force of a spring. The auxiliary main piston together with a part of the piston of the valve forms the parallel control throttle.